This invention relates to the use of compounds as inhibitors of the fatty acid synthase FabH.
The pathway for the biosynthesis of saturated fatty acids is very similar in prokaryotes and eukaryotes. However, although the chemical reactions may not vary, the organization of the biosynthetic apparatus is very different. Vertebrates and yeasts possess type I fatty acid synthases (FASs) in which all of the enzymatic activities are encoded on one or two polypeptide chains, respectively. The acyl carrier protein (ACP) is an integral part of the complex. In contrast, in most bacterial and plant FASs (type II) each of the reactions are catalyzed by distinct monofunctional enzymes and the ACP is a discrete protein. Mycobacteria are unique in that they possess both type I and II FASs; the former is involved in basic fatty acid biosynthesis whereas the latter is involved in synthesis of complex cell envelope lipids such as mycolic acids. There therefore appears to be considerable potential for selective inhibition of the bacterial systems by broad-spectrum antibacterial agents (Jackowski, S. 1992. In Emerging Targets in Antibacterial and Antifungal Chemotherapy. Ed. J. Sutcliffe and N. Georgopapadakou. Chapman and Hall, New York; Jackowski, S. et al. (1989). J. Biol. Chem. 264, 7624-7629.)
The first step in the biosynthetic cycle is the condensation of malonyl-ACP with acetyl-CoA by FabH. In subsequent rounds malonyl-ACP is condensed with the growing-chain acyl-ACP (FabB and FabF, synthases I and II respectively). The second step in the elongation cycle is ketoester reduction by NADPH-dependent xcex2-ketoacyl-ACP reductase (FabG). Subsequent dehydration by xcex2-hydroxyacyl-ACP dehydrase (either FabA or FabZ) leads to trans-2-enoyl-ACP which is in turn converted to acyl-ACP by NADH-dependent enoyl-ACP reductase (FabI). Further rounds of this cycle, adding two carbon atoms per cycle, eventually lead to palmitoyl-ACP whereupon the cycle is stopped largely due to feedback inhibition of FabH and I by palmitoyl-ACP (Heath, et al, (1996), J.Biol.Chem. 271, 1833-1836). FabH is therefore a major biosynthetic enzyme which is also a key regulatory point in the overall synthetic pathway (Heath, R. J. and Rock, C. O. 1996. J.Biol.Chem. 271, 1833-1836; Heath, R. J. and Rock, C. O. 1996. J.Biol.Chem. 271, 10996-11000).
The antibiotic thiolactomycin has broad-spectrum antibacterial activity both in vivo and in vitro and has been shown to specifically inhibit all three condensing enzymes. It is non-toxic and does not inhibit mammalian FASs (Hayashi, T. et al., 1984. J. Antibiotics 37, 1456-1461; Miyakawa, S. et al., 1982. J. Antibiotics 35, 411-419; Nawata, Y et al., 1989. Acta Cryst. C45, 978-979; Noto, T. et al., 1982. J. Antibiotics 35, 401-410; Oishi, H. et al., 1982. J. Antibiotics 35, 391-396. Similarly, cerulenin is a potent inhibitor of FabB and F and is bactericidal but is toxic to eukaryotes because it competes for the fatty-acyl binding site common to both FAS types (D""Agnolo, G. et al., 1973. Biochim. Biophys. Acta. 326, 155-166). Extensive work with these inhibitors has proved that these enzymes are essential for viability. Little work has been carried out in Gram-positive bacteria.
There is an unmet need for developing new classes of antibiotic compounds that are not subject to existing resistance mechanisms. No marketed antibiotics are targeted against fatty acid biosynthesis, therefore it is unlikely that novel antibiotics of this type would be rendered inactive by known antibiotic resistance mechanisms. Moreover, this is a potentially broad-spectrum target. Therefore, FabH inhibitors would serve to meet this unmet need.
This invention comprises indole derivatives and pharmaceutical compositions containing these compounds and their use as FabH inhibitors that are useful as antibiotics for the treatment of Gram positive and Gram negative bacterial infections.
This invention further constitutes a method for treatment of a Gram negative or Gram positive bacterial infection in an animal, including humans, which comprises administering to an animal in need thereof, an effective amount of a compound of this invention.
The compounds of this invention are represented by Formula (I): 
wherein:
R is selected from the group consisting of aryl, substituted aryl, heteroaryl or substituted heteroaryl; and
n is an integer from 0 to 6.
Also included in the invention are pharmaceutically acceptable salt complexes.
As used herein, xe2x80x9calkylxe2x80x9d means both straight and branched chains of 1 to 10 carbon atoms, unless the chain length is otherwise limited, including, but not limited to, methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, iso-butyl, tert-butyl, n-pentyl and the like. The alkyl may carry substituents such as hydroxy, carboxy, alkoxy, and the like.
The term xe2x80x9ccycloalkylxe2x80x9d is used herein to mean cyclic rings, preferably of 3 to 8 carbons, including but not limited to cyclopropyl, cyclopentyl, cyclohexyl, and the like.
The term xe2x80x9carylalkylxe2x80x9d or xe2x80x9cheteroarylalkylxe2x80x9d or xe2x80x9cheterocyclicalkylxe2x80x9d is used herein to mean C1-10 alkyl, as defined above, attached to an aryl, heteroaryl or heterocyclic moiety, as also defined herein, unless otherwise indicated.
As used herein, xe2x80x9carylxe2x80x9d means phenyl and naphthyl and substituted aryl such as hydroxy, carboxy, halo, alkoxy, methylenedioxy, and the like.
As used herein, xe2x80x9cheteroarylxe2x80x9d means a 5-10 membered aromatic ring system in which one or more rings contain one or more heteroatoms selected from the group consisting of N, O or S, such as, but not limited, to pyrrole, pyrazole, furan, tihiophene, quinoline, isoquinoline, quinazolinyl, pyridine, pyrimidine, oxazole, thiazole, thiadiazole, triazole, imidazole, and benzimidazole.
As used herein, preferred aryl substituents include halo, including chloro, fluoro, bromo and iodo, in any combination; C1-10alkyl, C1-10alkoxy, aryloxy, or heteroaryloxy.
The compounds of this invention may contain one or more asymmetric carbon atoms and may exist in racemic and optically active forms. All of these compounds and diastereomers are contemplated to be within the scope of the present invention.
Some of the compounds of this invention may be crystallised or recrystallised from solvents such as organic solvents. In such cases solvates may be formed. This invention includes within its scope stoichiometric solvates including hydrates as well as compounds containing variable amounts of water that may be produced by processes such as lyophilisation.
Since the antibiotic compounds of the invention are intended for use in pharmaceutical compositions it will readily be understood that they are each provided in substantially pure form, for example at least 60% pure, more suitably at least 75% pure and preferably at least 85%, especially at least 95% pure, particularly at least 98% pure (% are on a weight for weight basis). Impure preparations of the compounds may be used for preparing the more pure forms used in the pharmaceutical compositions; these less pure preparations of the compounds should contain at least 1%, more suitably at least 5% and preferably from 10 to 49% of a compound of the formula (I) or salt thereof.
Preferred compounds of the present invention include: 5-(2-chloro-5-hydroxybenzyloxy)-1-[(2-thiophen-3-yl)ethyl]-1H-indole-2-carboxylic acid; and 1-[(6-chlorobenzo[1,3]dioxol-5-yl)methyl]-5-(2-chloro-5-hydroxybenzyloxy)-1H-indole-2-carboxylic acid.
Compounds of formula (I) were prepared by the method described in Schemes 1 and 2. 
a) 10% Pd/C, H2, EtOH; b) allyl bromide, Cs2CO3, DMF; c) 2-(3-thienyl)ethanol, TMAD, Bu3P, THF; d) Pd(Ph3P)4, morpholine, H2O, CH2Cl2; e) 10, Cs2CO3, DMF; e) 1N NaOH, THF, EtOH
Indole ethyl ester 1, Scheme 1, (Aldrich) was debenzylated via catalytic hydrogenation to provide the 5-hydroxy indole 2. The 5-hydroxyl was then protected by alkylation with allyl bromide using a base such as cesium or potassium carbonate in an aprotic solvent such as DMF, thus, providing allyl ether 3. The indole nitrogen of 3 was next alkylated with the desired moiety using either standard alkylation conditions (alkyl halide and base) or, as illustrated herein, by using a Mitsunobu-type coupling reaction. Specifically, by reacting 3 with 2-(3-thienyl)ethanol in the presence of TMAD and tributylphosphine in THF, the desired product 4 was obtained. In this reaction, the 2-(3-thienyl)ethanol may be replaced by any desired alkyl alcohol allowing other analogs to be readily prepared. Removal of the allyl ether protecting group was achieved by exposure of 4 to the catalyst Pd(Ph3P)4, morpholine and water to provide the 5-hydroxy indole 5. Reaction of 5 with the benzyl bromide 10 (see Scheme 2) under standard conditions using a carbonate as base provided 6. In this instance, cesium carbonate was once again utilized. The benzenesulfonate of 6 was removed concomitantly with the ethyl ester by saponification (NaOH, THF, EtOH) to give the disired final product 7.
Benzyl bromide 10 was prepared as outlined in Scheme 2. 
a) PhSO2Cl, Et3N, CH2Cl2; b) NBS, CCl4, reflux
2-Chloro-5-hydroxytoluene (Aldrich) 8 was converted to the benzene sulfonate ester 9 by reaction with benzene sulfonyl chloride in the presence of triethylarnine. Benzylic brornination of 9, providing 10, was achieved using NBS in refluxing carbon tetrachloride.
Any of these compounds can potentially be used to treat any disease caused by pathogens that possess a type II fatty acid synthesis pathway, such as mycobacteria. Such diseases include, but are not limited to, malaria and tuberculosis.
The invention will now be described by reference to the following examples which are merely illustrative and are not to be construed as a limitation of the scope of the present invention. All temperatures are given in degrees centigrade, and all solvents are highest available purity unless otherwise indicated.